Application Of Phase Equilibrium Modeling In Metamorphic Rocks

With the development and improvement of thermodynamic database and component-activity model,the equilibrium simulation of metamorphic facies has gradually become a better method to constraint the temperature and pressure of metamorphic rocks.The theoretical basis is the thermodynamic equilibrium principle and the law of conservation of mass.At the same time,using the internal thermodynamic database and the corresponding composition-activity model,in a specific model system,the specific rock composition is calculated according to the profile view,and the minerals are obtained at the same time The isoline of the composition,combined with the petrographic characteristics of the rock,chemical characteristics of minerals,etc.,to obtain the temperature and pressure conditions of the rock.Metamorphic phase equilibrium research is to study the relationship between metamorphic mineral combinations in a rock system and the composition and metamorphic P-T conditions of a rock system according to the phase law and related thermodynamic equations.In this paper,the calculation of the visual profile of the North China Craton pelitic granulite and jadeite-lawsonite quartzite in the Dominican Republic is carried out.Metamorphic phase equilibrium calculation program THERMOCALC V340 was used to calculate the metamorphic conditions and metamorphic P-T trajectory of the North China Craton pelitic granulite.The system was NCKFMATSHO and the database was ds62.The data used for the calculation are the results of XRF testing of the whole rock composition.From the P-T pseudosection,it can be seen that the pressure peak conditions of the pelitic granulite in the North China Craton Huangtuyao are?13.8-14.1 kbar,?840-850 ?;and the temperature peak conditions of the pelitic granulite is?7kbar,?910?,combined with the results of the feldspar thermometer,the peak temperature conditions are limited to?7-7.2 kbar,909-915?;the metamorphic P-T trajectory of the pelitic graulite is a clockwise metamorphic P-T trajectory.Metamorphic phase equilibrium calculation program Preple_X(6.7.4)was used to calculate the metamorphic conditions of the jadeite-lawsonite quartzite in the Dominican Republic.The system is MnNCKFMATSHO,the thermodynamic database is dp04,and the temperature range of the diagram is 320-500?,the pressure range is 12-20kbar.The data used for the calculation is the effective whole rock component calculated by the minerals of peak period.From the P-T pseudosection,it can be seen that the combination of metamorphic minerals in the peak period of jadeite-lawsonite quartzite in the Dominican Republic is Grt+Law+Opx+ Q+Amph+Mu+Ru.The XMg of garnet(XMg=0.26)and Si of muscovite(Si=3.43)were used to constraint the temperature and pressure conditions of the peak period is 420?,18.2kbar.